In 2004, our practice was involved in documenting an important toxin for horses—fall Panicum (Panicum dichotomiflorum) grass. This common native grass has been fed to horses in hay and in pasture probably since the Europeans first brought horses to our area. But, while we know that it doesn’t cause illness all the time, certain growing conditions can cause it to become toxic, as it did in Nokesville, VA in 2004. We don’t know what triggers the grass to become toxic, but we do know that it sometimes does become toxic, and the conditions are right this year. This study proved the hepatotoxicity: http://www.ncbi.nlm.nih.gov/m/pubmed/17186859/

Currently, there are several cases of liver disease in Fauquier, Clark and Loudon counties that appear to be from grazing Panicum grass in the pasture. Some signs of toxicity from eating the grasses includes: decreased appetite, lethargy, somnolence (unusual periods of sleepiness), mild colic, or neurological signs. Some horses have no symptoms at all.

If you have this plant in your pasture or if you find it in your hay cut this year, you may want to have your horses tested for liver disease; this involves a simple blood draw. Call us at 703-754-3309 if you would like us to consult on a case you think might be panicum toxicosis, or if you just would like blood work on your horse to be sure. You can also consult your County Extension agent if you need help with plant identification.

18 yr old Arabian gelding showed elevation of GGT at 31 U/L. All other findings are within the normal range or at the lower end of normal range. My vet suspects panicum. First clue that something was not right was Wednesday evening when I found him lying down which he does not usually do in his stall. We thought he was suffering from gas pockets so took away his hay, called the vet who said to give him 8 cc banamine. Thursday he was hanging his head and obviously uncomfortable. Vet checked him out and his vitals were normal. Rushed the blood sample to the lab and got the report that showed GGT elevation at 31 U/L. I don’t really know what that means, but was told that his liver enzymes were “slightly” elevated. Ordered beet pulp and SMZs. He was uncomfortable so vet authorized 6 cc banamine and we let him graze. After that dose, he seemed considerably better. This morning (Friday) he had cleaned up the prescribed beet pulp as well as the feed with SMZs and was impatient for breakfast! He cleaned that up as well as tonight’s dinner. It’s as though there was never an issue! He was given hay today that has been checked for the panicum. My hope and prayer is that he did not suffer liver damage and will continue to be his normal self. My huge question is, is the entire panicum plant suspect or just the seed end? I’m concerned that we may have missed the stem parts! Thank you so very much for sharing your findings!!!

At this time no one knows for sure what part of the plant is toxic.
We hope your horse recovers quickly! There are many causes of a mildly elevated GGT, many of which are benign. It sounds like you will do any appropriate follow up if your horse does not continue to recover more. It is encouraging that your vet knew to include panicum in her diagnosis list.